The present invention relates to a process for the preparation of acetoacetylated aromatic amines, in particular of acetoacetylated N-phenyl-p-phenylenediamines, and novel acetoacetylated N-phenyl-p-phenylenediamines.
U.S. Pat. No. 2,115,413 describes the reaction of ethyl acetoacetate with N-phenyl-p-phenylenediamine for the preparation of 3-oxo-N-[4-(phenylamino)phenyl]-butyramide.
C. E. Kaslow et al. describes the reaction of primary aromatic amines with diketene for the preparation of acetoacetanilides in J. Am. Chem. Soc. 1946, 68, 644-647.
C. E. Kaslow et al. describes the reaction of secondary aromatic amines with diketene for the preparation of N-alkylacetoacetanilides in J. Am. Chem. Soc. 1945, 67, 1969-1970. The reaction is also described by N. Etkin et al. in J. Org. Chem. 1990, 55, 1093-1096. The secondary aromatic amines employed here are alkyl- or alkoxy-substituted anilines. The reaction of Nxe2x80x94C1-6-alkyl-3-oxo-N-[4-(phenylamino)phenyl]butyramides is not described.
The object of the present invention was to make available a process for the preparation of acetoacetylated N-phenyl-p-phenylenediamines. The object is achieved by the process of the invention.
The process relates to the preparation of compounds of the general formula 
in which
R1 and R2 are at each occurrence independently hydroxyl, C1-6-alkyl, C1-6-alkoxy, halogen, phenyl or phenoxy;
R3 is hydrogen or C1-6-alkyl.
m is an integer from 0 to 4; and
n is an integer from 0 to 5.
These compounds can exist in at least two tautomeric forms (keto-enol tautomerism), whereas for simplification only the keto form, respectively, is mapped here. However, the invention comprises all tautomers and their mixtures.
The process is characterized in that diketene is reacted with an N-phenyl-p-phenylenediamine of the general formula 
in which R1, R2, R3, m and n have the meaning indicated above, in the presence of 3-40% strength acetic acid at temperatures of 20 to 100xc2x0 C., preferably at 60 to 70xc2x0 C.
C1-6-Alkyl is understood here and below as meaning all linear or branched alkyl groups having 1-6 carbon atoms such as, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, tert-pentyl, neopentyl, hexyl or isohexyl.
C1-6-Alkoxy is understood as meaning groups which are composed of C1-6-alkyl and oxygen, such as, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, sec-butoxy or tert-butoxy.
The variables m and n have preferably the value 0 (zero). The radical R3 is preferably C1-6-alkyl, particularly preferably isopropyl.
The addition of the diketene surprisingly only takes place at the nitrogen atom which carries the radical R3.
The compound of the formula II in which m=n=0 and R3 is hydrogen are commercially obtainable, e.g. from Fluka, the remaining compounds can be prepared according to known methods, e.g. by reaction of aniline or substituted aniline with nitrobenzene or azobenzene and subsequent hydrogenation. The compounds of the formula II in which R3 is C1-6-alkyl can be prepared according to known methods, e.g. by reductive alkylation of N-phenyl-p-phenylenediamines of the formula II (R3xe2x95x90H) with an aliphatic ketone or aldehyde.
The compounds of the formula I in which R3 is C1-6-alkyl are novel and likewise a subject of the invention. These compounds can be employed, for example as additives for fuels of internal combustion engines. A further possibility of use is afforded as drying accelerators for polymers.
The compounds of the formula I can be converted by reaction with ammonia into the corresponding enamines of the general formula 
in which R1, R2, R3, m and n have the meaning indicated above. These enamines can exist as two geometric isomers (E and Z-configuration at the enamine double bond), whereas here the two isomers as well as their mixtures are comprehended. Preferably, the Z-configuration is formed.
The reaction with ammonia is expediently carried out at temperatures from 10 to 150xc2x0 C., preferably at approximately 70xc2x0 C., and pressures from 1 to 100 bar, preferably at 10 to 30 bar. The reaction is expediently carried out in a suitable solvent in the presence of catalytic amounts of conc. or aqueous acetic acid. Suitable solvents are, for example, esters, aromatic and aliphatic hydrocarbons, chlorinated aliphatic hydrocarbons, ethers and polyethers, alcohols and also water. Preferably, ethyl acetate is employed as a solvent. Expediently, 0.02-2.0 mol of conc. acetic acid are employed based on 1 mol of the compound of the formula I.
The compounds of the formula III in which R3 is C1-6-alkyl are novel and likewise a subject of the invention.
By means of catalytic hydrogenation of the compounds of the formula III, compounds of the general formula 
in which R1, R2, R3, m and n have the meaning indicated above, are formed.
The catalytic hydrogenation is carried out at temperatures from 100 to 200xc2x0 C., preferably at approximately 110xc2x0 C., and pressures of 20 to 150 bar, preferably of approximately 100 bar. A suitable hydrogenation catalyst is Raney nickel. The hydrogenation is expediently carried out in a suitable solvent in the presence of a base, preferably in the presence of ammonia. Suitable solvents are for example aliphatic alcohols or mixtures of water and aliphatic alcohols, methanol being preferably employed.
The compounds of the formula IV in which R3 is C1-6-alkyl are novel and likewise a subject of the invention.
The following examples illustrate the implementation of the process according to the invention and the preparation of the compounds according to the invention, without being regarded as restricting them.